Get past migrations from add-on.

{
  "type": "array",
  "items": {
    "type": "object",
    "properties": {
      "addon_id": {
        "type": "string"
      },
      "callback_url": {
        "type": "string"
      },
      "database": {
        "type": "string"
      },
      "database_user": {
        "type": "string"
      },
      "dump_restore_finished_date": {
        "type": "string"
      },
      "dump_restore_start_date": {
        "type": "string"
      },
      "end_date": {
        "type": "string"
      },
      "exit_message": {
        "type": "string"
      },
      "hostname": {
        "type": "string"
      },
      "id": {
        "type": "string"
      },
      "kind": {
        "type": "string"
      },
      "last_state_update_date": {
        "type": "string"
      },
      "new_cluster_id": {
        "type": "string"
      },
      "new_cluster_label": {
        "type": "string"
      },
      "new_instance_id": {
        "type": "string"
      },
      "new_plan": {
        "type": "string"
      },
      "new_recipient_hostname": {
        "type": "string"
      },
      "new_zone": {
        "type": "string"
      },
      "old_cluster_id": {
        "type": "string"
      },
      "old_cluster_label": {
        "type": "string"
      },
      "old_instance_id": {
        "type": "string"
      },
      "old_plan": {
        "type": "string"
      },
      "old_recipient_hostname": {
        "type": "string"
      },
      "old_zone": {
        "type": "string"
      },
      "port": {
        "type": "number"
      },
      "request_date": {
        "type": "string"
      },
      "state": {
        "type": "string"
      }
    }
  }
}